The adaptive optics system for the Thirty Meter Telescope (TMT) is the Narrow-Field InfraRed Adaptive Optics System (NFIRAOS). Recently, INO has been involved in the optomechanical design of several subsystems of NFIRAOS, including the Instrument Selection Mirror (ISM), the NFIRAOS Beamsplitters (NBS), and the NFIRAOS Source Simulator system (NSS) comprising the Focal Plane Mask (FPM), the Laser Guide Star (LGS) sources, and the Natural Guide Star (NGS) sources. This paper presents an overview of these subsystems and the optomechanical design approaches used to meet the optical performance requirements under environmental constraints.
The early-light facility adaptive optics system for the Thirty Meter Telescope (TMT) is the Narrow-Field InfraRed Adaptive Optics System (NFIRAOS). The science beam splitter changer mechanism and the visible light beam splitter are subsystems of NFIRAOS. This paper presents the opto-mechanical design of the NFIRAOS beam splitters subsystems (NBS). In addition to the modal and the structural analyses, the beam splitters surface deformations are computed considering the environmental constraints during operation. Surface deformations are fit to Zernike polynomials using SigFit software. Rigid body motion as well as residual RMS and peak-to-valley surface deformations are calculated. Finally, deformed surfaces are exported to Zemax to evaluate the transmitted and reflected wave front error. The simulation results of this integrated opto-mechanical analysis have shown compliance with all optical requirements.
Wavefront sensing is one of the key elements of an Adaptive Optics System. Although Shack-Hartmann WFS are the
most commonly used whether for astronomical or biomedical applications, the high-sensitivity and large dynamic-range
of the Pyramid-WFS (P-WFS) technology is promising and needs to be further investigated for proper justification in
future Extremely Large Telescopes (ELT) applications. At INO, center for applied research in optics and technology
transfer in Quebec City, Canada, we have recently set to develop a Pyramid wavefront sensor (P-WFS), an option for
which no other research group in Canada had any experience. A first version had been built and tested in 2013 in
collaboration with NRC-HIA Victoria. Here we present a second iteration of demonstrator with an extended spectral
range, fast modulation capability and low-noise, fast-acquisition EMCCD sensor. The system has been designed with
compactness and robustness in mind to allow on-sky testing at Mont Mégantic facility, in parallel with a Shack-
Hartmann sensor so as to compare both options.
With the commencement of shared-risk science observations in May 2012, the Keck I laser guide star (LGS) adaptive
optics (AO) system is the second LGS AO system to be commissioned at the W. M. Keck Observatory. This paper
reports on the Keck I LGS AO system itself and some of the initial performance results. The Keck I system differs from
the Keck II system primarily with regards to the laser and a beam transport system which projects the laser from behind
the telescope’s secondary mirror. The existing OSIRIS science instrument has been integrated with the Keck I system.
Ground-baseed long baselinne interferomeeters have lonng been limiteed in sensitiviity by the shoort integration periods imposed by atmospheric tuurbulence. Thee first observaation fainter thhan this limit wwas performedd on January 222, 2011 when the Keck Interferommeter observedd a K=11.5 taarget, about onne magnitude fainter than iits K=10.3 limmit. This observation wwas made posssible by the Duual Field Phase Referencing instrument of the ASTRA pproject: simultaaneously measuring thhe real-time efffects of the atmmosphere on a nearby bright guide star, andd correcting foor it on the fainnt target, integration tiime longer thaan the turbulennce time scale are made possible. As a preelude to this ddemonstration, we first present the implementatioon of Dual FField Phase RReferencing onn the interferoometer. We tthen detail itss on-sky performance focusing on tthe accuracy oof the turbulennce correction, and on the reesulting fringe contrast stabiility. We conclude witth a presentatioon of early resuults obtained wwith Laser Guidde Star AO andd the interferommeter.
ASTRA (ASTrometric and phase-Referencing Astronomy) is an upgrade to the existing Keck Interferometer
which aims at providing new self-phase referencing (high spectral resolution observation of YSOs), dual-field
phase referencing (sensitive AGN observations), and astrometric (known exoplanetary systems characterization
and galactic center general relativity in strong field regime) capabilities. With the first high spectral resolution
mode now offered to the community, this contribution focuses on the progress of the dual field and astrometric modes.
The Laser Guide Star commissioned in 2007 at the WHT on La Palma is based on Rayleigh backscattering of a 515 nm
beam provided by a diode pumped Q-switched doubled frequency Yb:YAG laser launched from behind the WHT
secondary mirror. At the time the laser beam is focused at a distance of 15km above the telescope ground and its power
just under 20W. With such a pulsed laser, careful fine tuning of the range gate system is essential to isolate the most
focused part of the LGS and eliminate parts of the laser plume which would degrade the Shack-Hartmann spots and
consequently AO correction. This is achieved by an electro-optic shutter using Pockels cells, triggered by a delay
generator synchronised on the laser pulses, and by spatial filters. Images of 0.15" resolution in J and H bands, very close
to expected performance, have been routinely taken as soon as the third and fourth commissioning runs. Here we show
the performance of the range gate system as measured and improved over the successive commissioning runs, as well as
the off sky and on sky calibration procedures of the LGS AO system.
GLAS (Ground-layer Laser Adaptive optics System) provides a Rayleigh Laser Guide Star (LGS) upgrade to the existing
NAOMI AO system at the 4.2-m William Herschel Telescope on La Palma. Installation of the GLAS upgrades
commenced in 2006 with on-sky commissioning taking place from May 2007. Commissioning was very successful and
AO correction was first observed during the August 2007 observing run. Here we present an overview of the opto-mechanical
systems that have been installed and commissioned, including the LGS launch system, LGS safety systems
and LGS Wave Front Sensor, concentrating on the integration of the various optical and optoelectronic components.
GLAS is an upgrade of the William Herschel Telescope's existing natural-guide-star (NGS) AO system NAOMI
to incorporate a 20-W Rayleigh laser guide star (LGS) projected to an altitude of 15 km. It is currently being
commissioned on-sky, and we review here the current status of the project. GLAS/NAOMI delivers dramatic
improvements in PSF in both the near-IR (AO-corrected FWHM close to the diffraction limit, >~ 0.15 arcsec)
and in the optical (factor of ~ 2 reduction in FWHM). The performance is similar to that with NGS, and is
consistent with predictions from modelling. The main advantage over NGS AO is the large gain in sky coverage
(from ~ 1% to ~ 100% at galactic latitude 40°). GLAS provides the first on-sky demonstration of closed-loop
ground-layer AO (GLAO), and is the first Rayleigh LGS AO system to be offered for general use, at any telescope.
NAOMI is the AO system of the 4.2-m William Herschel Telescope on La Palma. It delivers near-diffraction-limited images in the IR, and a significantly improved PSF at optical wavelengths. The science cameras currently comprise an IR imager (INGRID), an optical integral-field spectrograph (OASIS) and a coronagraph which may be placed in the light path to either instrument. 19 science programmes were observed during 2002-3. Observing overheads are small, with as much as 60% of the night spent integrating on science targets. In late 2004 this year, the WFS will be equipped with a low-noise L3 CCD, giving a gain of a factor of 2 in S:N for faint guide stars. A Rayleigh laser guide star is under development, with first light expected summer 2006, providing a unique facility: AO-corrected optical integral-field spectroscopy anywhere on the northern sky.
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